M Zeeshan Chaudhry, Gabrielle T Belz
Research in 2025 demonstrated that memory and exhausted CD8+ T cell lineages arise from shared TCF1+ progenitors and that fate divergence is actively enforced by transcriptional programs rather than fixed at priming. Multi-state regulators such as KLF2 and GFI1 preserve stemness, restrain exhaustion, and calibrate differentiation under acute and chronic antigenic stress. CD8+ T cells are a central component of the adaptive immune system that control pathogens and cancer. Following activation, CD8+ T cells differentiate into specialized subsets, including cytotoxic effector cells that eliminate aberrant cells and stem-like memory cell populations endowed with self-renewal capacity and long-term persistence.1, 2 This differentiation process is tightly regulated by transcription factors to balance the immediate pathogen clearance with the establishment of durable memory cells that retain stemness and robust recall potential.2 In the case of chronic viral infections, where the virus is not rapidly cleared from the body, sustained antigenic stimulation skews CD8+ T cell differentiation toward an exhausted Tcell state3 characterized by elevated inhibitory receptor expression, such as programmed cell death 1 receptor (PD1). This adaptation protects host tissues from excessive immunopathology but comes at the cost of reduced stemness and long-term persistence.4 Significant progress has been made in defining the transcription networks that govern CD8+ T cell fate decisions, with important implications for next-generation immunotherapies. Here, we highlight key studies from 2025 that advance our understanding of the transcriptional mechanisms preserving CD8+ T cell stemness and shaping differentiation under conditions of acute and chronic antigenic stress. Stem-like memory CD8+ T cells (TSCM) represent a self-renewing pluripotent population that gives rise to cytotoxic effector cells and sustains durable antiviral memory responses. In contrast, exhausted CD8+ T cell (TEX) responses during sustained antigenic stimulation are maintained by progenitors of exhausted (Tpex) cells, typically defined as PD1+TCF1+TOX+. Tpex cells arise early during persistent antigenic stimulation and were previously considered unique to chronic infection or tumors, highlighting a distinct progenitor hierarchy between acute and chronic immune responses. Two complementary studies from Ahmed5 and Zehn6 laboratories challenged this view by demonstrating that TCF1+ progenitors arising early during acute lymphocytic choriomeningitis virus (LCMV) infection are heterogeneous and contain cells with transcriptional and epigenetic features of both memory and exhaustion lineages (Figure 1). The generation of Tpex-like progenitors during acute LCMV infection required strong TCR stimulation, as low-affinity TCR-antigen interactions failed to produce this population.6 The fate of the precursor CD8+ T cells was highly context-dependent, such that Tpex cells generated during acute infection differentiated into exhausted T cells when transferred into chronically infected hosts, whereas stem-like CD8+ T cells isolated from chronic LCMV infection acquired memory characteristics following transfer into acutely infected mice.5 Together, these studies demonstrate that memory and exhausted CD8+ T cell lineages share a common early progenitor pool with fate determined by the duration and intensity of antigenic stimulation, highlighting a unified progenitor hierarchy linking T cell responses to acute and chronic virus infection. While recent studies established that memory and exhausted CD8+ T cell lineages originate from a shared pool of early TCF1+ progenitors, the mechanisms that preserve lineage fidelity and sustain CD8+ T cell stemness remain incompletely understood. Fagerberg et al.7 used a Perturb-seq approach, combining in vivo CRISPR-mediated perturbation with single-cell RNA-seq, to identify Krüppel-like factor 210 (KLF2) as a critical regulator that preserves stem-like CD8+ T cell identity and suppresses exhaustion programs during acute viral infection (Figure 1). In an acute LCMV infection model, KLF2 was shown to restrain exhaustion-associated transcriptional programs, thereby maintaining lineage fidelity of stem-like CD8+ T cells and preventing premature adoption of an exhausted fate. Loss of KLF2 resulted in a marked reduction in cytotoxic effector production, including granzyme A and perforin, accompanied by upregulation of inhibitory receptors such as PD-1. Interestingly, KLF2-deficient cells exhibited an exhaustion-linked transcriptional profile despite efficient viral clearance, indicating that exhaustion is not merely a consequence of chronic antigen exposure but must be transcriptionally suppressed during acute responses. Mechanistically, KLF2 functioned downstream of TCR signaling to enhance T-BET and limit TOX expression, a known regulator of CD8+ T cell exhaustion,11 thereby limiting TOX-dependent exhaustion pathways. Moreover, Zhu et al.8 showed that KLF2 restricts Pdcd1 and Tox expression in tumor-infiltrating T cells.7, 8 These results demonstrate that KLF2 suppresses exhaustion-related gene expression during acute viral infection and limits the extent of exhaustion under chronic antigenic stimulation. Although KLF2 expression decreases following sustained TCR signaling, a systematic analysis across acute and chronic infectious contexts will be required to identify upstream regulators of KLF2 activity. Complementing these findings, enhancer-driven gene regulatory network analysis by Green et al.12 revealed that KLF2 also actively represses the differentiation of tissue-resident memory(TRM)-like tumor-infiltrating T cells, thereby limiting acquisition of a residency-associated program linked to potent anti-tumor function. Downregulation of KLF2 enabled TRM-like tumor-infiltrating T cell formation, whereas sustained expression limited this differentiation axis in the tumor microenvironment. These findings establish KLF2 as a multi-state transcription factor with distinct yet coordinated roles across CD8+ T cell differentiation states. Integrating these findings with recent progenitor fate-mapping studies5, 6 supports a unified model in which early CD8+ T cell precursors retain plasticity toward memory or exhaustion lineages, while transcription factors such as KLF2 enforce context-appropriate fate decisions.7, 8 By suppressing exhaustion programs during acute infection while permitting effector differentiation, KLF2 ensures durable memory formation and prevents maladaptive lineage deviation, with direct implications for optimizing T cell immunotherapies. Recent work in 2025 identified growth factor independent 113 (GFI1) as a multi-faceted regulator that reinforces stem-like identity while shaping CD8+ T cell differentiation trajectories under chronic antigenic stress. Chaudhry et al.14 demonstrated that GFI1-driven transcriptional and epigenetic programs maintain CD8+ T cell stemness and persistence across distinct chronic infections, including one that induces CD8+ T cell exhaustion (LCMV)4 and another characterized by continuous accumulation of terminally differentiated effector T cells (mouse cytomegalovirus).9, 15 Elevated GFI1 expression in stem-like CD8+ T cells (TCF1+CX3CR1−) enhanced their proliferative capacity, thereby supporting the persistence of virus-specific responses. Mechanistically, GFI1 sustained memory-associated genes, including Tcf7 and Eomes, and promoted survival of CD8+ T cells by inducing BCL-2 expression in an EOMES-dependent manner. Accordingly, loss of GFI1 resulted in progressive depletion of memory populations, illustrating its central role in maintaining durable CD8+ T cell stemness. Moreover, tamoxifen-mediated GFI1 deletion in virus-specific CD8+ T cells during chronic virus infection further demonstrated that continuous expression of GFI1 is required to preserve long-term CD8+ T cell responses. Consistent with these findings, Ojo et al.16 reported that GFI1 expression is restricted to virus-specific and tumor-infiltrating stem-like precursor cells during chronic virus infection and tumor challenge. Extending this framework, Chung et al.17 identified GFI1 as a shared regulator of exhausted and tissue-resident CD8+ T cells, highlighting its broader involvement in lineage-selective differentiation circuits rather than exclusively in stem-like maintenance. Collectively, these studies establish GFI1 as a central transcriptional node that sustains stem-like identity while calibrating differentiation trajectories during chronic antigen exposure. However, the upstream mechanisms controlling GFI1 expression and activity remain poorly defined. Notably, disruption of TCR signaling did not alter GFI1 expression,14 suggesting that its regulation may be uncoupled from canonical TCR-dependent transcriptional programs. Defining the signals that control GFI1 dynamics will therefore be critical for understanding how durable CD8+ T cell responses are sustained during chronic immune challenges. Collectively, the studies highlighted here refine our understanding of CD8+ T cell fate determination by supporting a unified developmental framework in which memory and exhausted lineages arise from shared early progenitors and are subsequently shaped by context-dependent transcriptional control. Evidence from 2025 establishes that lineage divergence is not hard-wired at priming but is actively enforced by multi-state transcription factors such as KLF2 and GFI1, which integrate environmental cues to preserve stemness, restrict exhaustion, and calibrate differentiation under acute and chronic antigenic stress. KLF2 acts early to suppress exhaustion and tissue-resident programs, thereby maintaining lineage fidelity, whereas GFI1 sustains proliferative capacity and long-term persistence of stem-like CD8+ T cells while also shaping differentiation within exhausted and tissue-resident compartments. Together, these findings emphasize that CD8+ T cell plasticity is actively sustained through continuous transcriptional regulation rather than driven solely by antigen exposure, providing a conceptual foundation for therapeutic strategies aimed at stabilizing stem-like states to enhance durable immunity. The authors declare no conflicts of interest. Conceptualization: M.Z.C. Writing – original draft: M.Z.C. and G.T.B.